Colored "frames" bug with CA correction

[komtur]

When I use Chromatic Aberration Correcton on any RAW file, everything goes fine in ASP, but the resulting file (TIFF) saved on disk has ugly red / green thin borders (especially at the left side of image).
I wonder if there is any way to avoid this problem temporary.

[rawshoter]

I to have those 1 pixel wide red lines at the image edges.
And in addition, on my images there are vertical and horizontal lines across the entire image.

They only appear when the CA correction is in use. And thy are visible in ASP as well as on the exported Jpeg file.

[Rob Greenstein]

Is the on screen image (revealing the vertical and horizontal fracture lines) being viewed at 1:1 100%?

Are the same artifacts also present in any generated TIFF and JPG output files?

[komtur]

Is the on screen image (revealing the vertical and horizontal fracture lines) being viewed at 1:1 100%?
Are the same artifacts also present in any generated TIFF and JPG output files?

In my case, when I'm looking at the image in ASP, everything is OK - no lines, no colored borders.
I have these artifacts (lines and borders) only in generatedt TIFFs and JPEGs.

[rawshoter]

Is the on screen image (revealing the vertical and horizontal fracture lines) being viewed at 1:1 100%?

Yes and they are only visible at 1:1.

Are the same artifacts also present in any generated TIFF and JPG output files?

Yes they are, though they are not always easy to find. And it strongly depends on the content of the image. You can´t find them on a pure blue sky for instance. But it´s not file type related because you can see them already in ASP.

Well, what I found out so far.
There are always two lines crossing the image right from the center. To find them, you need to set the ASP sharpening at minimum 200 better 300 or more and one of the CA correction channels at some value other than zero. (I set R/C to +0,030 ). Any denoising must be set off, because it makes it harder to find the artifacts.
Now find the center of the image and beginning from there, go to left, right, up and down, and look for the offset line/artifacts. It is helpful if you place a grid line in your image editor near the center of the image and oversharpen the image a little bit, to boost the phenomenon.

At this way, I could find the artifacts on Nikon D5100, Canon EOS 5D and on Powershot G10 files.

I guess, that for the CA correction, ASP divides the image into 4 parts and shift them against each other to get the color offset back on track. The resulting misalignment of this 4 blocks causes the artifacts. But again, this is just my humble guess.

EOS 5D

Powershot G10

[tomsi42]

Does the frames disappear if you turn of the native ASP sharpening?

[rawshoter]

Does the frames disappear if you turn of the native ASP sharpening?

I think we have to distinguish between two different phenomenons occuring by the CA correction.
One are the colored lines at the edges of the image described by komtur. I observed them to on some of my images, but can´t reproduce them reliably.

And the other one are the 2 artifact lines crossing the center of the image.
This one doesn´t disappear if I turn of the sharpening. But they obviously become less visible because of the blurring effect.

Can you, or someone else, reproduce this?

[tomsi42]

I think we have to distinguish between two different phenomenons occuring by the CA correction.

I see.

One are the colored lines at the edges of the image described by komtur. I observed them to on some of my images, but can´t reproduce them reliably.

I hadn't heard about this one.

And the other one are the 2 artifact lines crossing the center of the image.
This one doesn´t disappear if I turn of the sharpening. But they obviously become less visible because of the blurring effect.

I have heard about this one, but haven't seen it myself. It's not only CA that can cause this, apparently. Other tools might also provoke this.

Can you, or someone else, reproduce this?

I can see if I am able to try this tonigh. I have files from multiple Canon, Nikon, Olympus and Panasonic cameras, so it should be possible to gather some useful information here.

[rawshoter]

One are the colored lines at the edges of the image described by komtur. I observed them to on some of my images, but can´t reproduce them reliably.

I hadn't heard about this one.

Here is an example of that.

The red line is located at the upper edge, it is 1 pixel wide and goes over the entire image. I blew up the screenshot to 300% to make it more visible.
In opposition to the artifacts bug, this edge or frame lines are only visible at the output files.

I can see if I am able to try this tonigh. I have files from multiple Canon, Nikon, Olympus and Panasonic cameras, so it should be possible to gather some useful information here.

In the meantime I got feedback on a german forum where someone could reproduce that on his Linux machine with a D90 file.

[tomsi42]

Here is an example of that.

-- 8< --

The red line is located at the upper edge, it is 1 pixel wide and goes over the entire image. I blew up the screenshot to 300% to make it more visible.
In opposition to the artifacts bug, this edge or frame lines are only visible at the output files.

Is it also visible when you do a crop?

In the meantime I got feedback on a german forum where someone could reproduce that on his Linux machine with a D90 file.

Ok. I still think I will have a little look.

[rawshoter]

Is it also visible when you do a crop?

No, then it´s vanished.

Ok. I still think I will have a little look.

Oh yes please. I don´t meant that further testing is not necessary.

[tomsi42]

Is it also visible when you do a crop?

No, then it´s vanished.

Then it should be easy to reproduce and fix. I suspect the CA algorythm expands the canvas to enable the bitshifting needed, but forgets to crop afterwards.

And that also explains why it's not always seen - if you straigthen you photo, a crop is applied. And if you crop yourself, it will be gone on at least one side. Lens correction will also apply a crop.

[spoilerhead]

i can reproduce it with crop on

looks like it is exactly in the center of the original image.

[tomsi42]

i can reproduce it with crop on

looks like it is exactly in the center of the original image.

The problem is that we are discussing two bugs in this thread...

And the bug, which you are thinking about, is not fixed by doing a crop. We are talking about the other one...

[rawshoter]

Lens correction will also apply a crop.

Are you sure?
If I do only CA correction, then the red line goes continuous from one corner to the other.
But if I additionally apply lens correction, where the corners are being pushed outside the canvas, then the red line only remains in the middle part of the image because the rest is just pushed out by the lens correction. So it depends on the amount and method of lens correction, whether the line completely disappears or not.